Scotty really must be much stronger than he looks. At one point in this episode, he knocks a Klingon unconscious by hitting him on the elbow!

Great Moment :

Kirk and the Kang laughing together, a truly surreal sight.

Body Count :

Lots, but they all are revived by the alien. Most of Kang's crew seem to have died for good either shortly before or during the episode.

Factoid :

Kang will re-appear in Deep Space Nine's "Blood Oath", this time complete with the ridged forehead which Klingons acquired in later years.

This episode is the first one in which we ever see a female Klingon.

This is the first time intra-ship beaming is used in Star Trek.

The Klingon agonizer is the exact same one as seen in use by the Terran Empire in "Mirror, Mirror."

With 38 Klingons captured and "over 400" of Kang's crew dead, we get the crew of a Klingon cruiser in this episode - 440 or so, just about the same as Kirk's ship.

Plotline

Responding to a distress call from the planet Beta XII-A, the Enterprise crew beam down to find no sign of civilisation on the planet. Spock calls Kirk to inform him of the approach of a Klingon battlecruiser, badly damaged. A group of Klingons beams down and takes Kirk and the landing party hostage. Their leader, kang, accuses Kirk of attacking his ship and claims the Enterprise in reperation. Meanwhile a strange energy cloud watches from nearby...

When Kang begins torturing the landing party Kirk acquiesces to his demand, but sends an emergency code to the ship when calling for transport. Scotty rematerialises the Enterprise crew whilst keeping the Klingons in transporter suspension, allowing Kirk to quickly capture them. Destroying the battlecruiser as a threat to navigation, Kirk proceeds on course - with the energy cloud stowing away on board. The ship quickly goes out of control, setting itself on a course straight out of the galaxy. Hundreds of crewmen are trapped on the lower decks, with a strange alteration in the metal rendering it impossible to burn through to release them. Kirk questions Kang about the mystery but whilst they are talking everyday items in the room transform into swords. The Klingons take the opportunity to escape in a fierce battle.

It soon becomes clear that both sides are evenly matched in numbers. Bizzarely, injured crewmen miracuously recover from moral wounds and are soon ready to join the fight again. Spock detects the mysterious energy cloud on board, determining it to be some sort of life form. Kirk concludes that the alien has created the entire situation, engineering a small war for its own benefit. He resolves to seek peace with the Klingons so that they can join forces against the real enemy.

Chekov manages to capture Kang's science officer, his wife Mara. Kirk manages to convince Mara of the true situation, and the pair beam to engineering to meet with Kang. Suspicious, Kang attacks Kirk and the two fight - until Kirk finally throws down his weapon, stating that even if Kang kills him the entity will simply revive him so that they can go on fighting forever. Kang realises the truth of his words and tosses aside his own weapon, refusing to be the puppet of an alien. Both Kirk and Kang order a ceasefire, and when the alien appears they begin mocking it, laughing and joking with one another. The alien, who has been feeding on the negative emotions the conflict has generated, is repelled by their actions and reluctantly leaves the ship. As the ship returns to its own space, Kirk ponders how many of the conflicts in Human history may have been created by such creatures, and how different things may be now that their existence is known.

Analysis

An interesting idea, this one. The alien is a bit too powerful for my tastes - the idea that it can transmute matter in such a controlled way is somewhat believable, but sealing the bulk of the Enterprise crew below decks and then altering the ship's structure so that they can't be released seems a bit silly. But the plot really couldn't have worked if the Klingons were outnumbered dozens to one, and having a few hundred Klingons aboard wasn't really feasible, so this was probably the only way to do it.

The best moments come with the crew feeling the effects of the creature, stirring up racial bigotry both against the Klingons and even between the Starfleet officers. Kirk's realisation of what is happening is a great moment, and his subsequent reaching out to the Klingons is excellent. It's a classic Trek message - that the enemy is not the real enemy, the real enemy is the hatred and distrust which is the root cause of the conflict. "The only thing we have to fear is fear itself — nameless, unreasoning, unjustified terror which paralyses needed efforts to convert retreat into advance," as FDR put it.

Of course, the episode is also notable in that it introduces us to Kang, who will appear several times in future incarnations of Trek. Kang is an excellent character for a baddie; he's not simply evil, just a man living by his own warrior code. He clearly loves his wife, yet he is willing to sacrifice her rather than let Kirk use her capture to blackmail him. And he clearly has his fair share of hatred for the Federation, yet he's more than willing to put it aside to fight the true enemy. A great character.